executor: add SHOW BUILTINS command (#12941)

executor/show.go

@@ -185,6 +185,8 @@ func (e *ShowExec) fetchAll(ctx context.Context) error {
 		return nil
 	case ast.ShowRegions:
 		return e.fetchShowTableRegions()
+	case ast.ShowBuiltins:
+		return e.fetchShowBuiltins()
 	}
 	return nil
 }
@@ -1327,3 +1329,10 @@ func (e *ShowExec) fillRegionsToChunk(regions []regionMeta) {
 		e.result.AppendInt64(10, regions[i].approximateKeys)
 	}
 }
+
+func (e *ShowExec) fetchShowBuiltins() error {
+	for _, f := range expression.GetBuiltinList() {
+		e.appendRow([]interface{}{f})
+	}
+	return nil
+}

executor/show_test.go

@@ -639,3 +639,13 @@ func (s *testSuite5) TestShowEscape(c *C) {
 	tk.MustExec("rename table \"t`abl\"\"e\" to t")
 	tk.MustExec("set sql_mode=@old_sql_mode")
 }
+
+func (s *testSuite5) TestShowBuiltin(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	res := tk.MustQuery("show builtins;")
+	c.Assert(res, NotNil)
+	rows := res.Rows()
+	c.Assert(262, Equals, len(rows))
+	c.Assert("abs", Equals, rows[0][0].(string))
+	c.Assert("yearweek", Equals, rows[261][0].(string))
+}

expression/builtin.go

@@ -24,6 +24,8 @@
 package expression
 
 import (
+	"sort"
+	"strings"
 	"sync"
 
 	"github.com/pingcap/errors"
@@ -775,3 +777,30 @@ func IsFunctionSupported(name string) bool {
 	_, ok := funcs[name]
 	return ok
 }
+
+// GetBuiltinList returns a list of builtin functions
+func GetBuiltinList() []string {
+	res := make([]string, 0, len(funcs))
+	notImplementedFunctions := []string{ast.RowFunc}
+	for funcName := range funcs {
+		skipFunc := false
+		// Skip not implemented functions
+		for _, notImplFunc := range notImplementedFunctions {
+			if funcName == notImplFunc {
+				skipFunc = true
+			}
+		}
+		// Skip literal functions
+		// (their names are not readable: 'tidb`.(dateliteral, for example)
+		// See: https://github.com/pingcap/parser/pull/591
+		if strings.HasPrefix(funcName, "'tidb`.(") {
+			skipFunc = true
+		}
+		if skipFunc {
+			continue
+		}
+		res = append(res, funcName)
+	}
+	sort.Strings(res)
+	return res
+}

planner/core/planbuilder.go

@@ -2822,6 +2822,9 @@ func buildShowSchema(s *ast.ShowStmt, isView bool) (schema *expression.Schema, o
 	case ast.ShowAnalyzeStatus:
 		names = []string{"Table_schema", "Table_name", "Partition_name", "Job_info", "Processed_rows", "Start_time", "State"}
 		ftypes = []byte{mysql.TypeVarchar, mysql.TypeVarchar, mysql.TypeVarchar, mysql.TypeVarchar, mysql.TypeLonglong, mysql.TypeDatetime, mysql.TypeVarchar}
+	case ast.ShowBuiltins:
+		names = []string{"Supported_builtin_functions"}
+		ftypes = []byte{mysql.TypeVarchar}
 	}
 
 	schema = expression.NewSchema(make([]*expression.Column, 0, len(names))...)